A magnet creates a magnetic field around it. You cannot see a magnetic field, but you can observe its effects. A force is exerted on a magnetic material brought into a magnetic field. The force is a non-contact force because the magnet and the material do not have to touch each other.
You can use a plotting compass or iron filings to detect a magnetic field:
It would be difficult to draw the results from the sort of experiment seen in the photograph, so we draw simple magnetic field lines instead.
In the diagram, note that:
The magnetic field is strongest at the poles, where the field lines are most concentrated.
Field lines also show what happens to the magnetic fields of two magnets during attraction or repulsion.